An AC vehicle generator of this type includes an armature coil and a field coil, and is driven by a motor, such as an engine equipped in the vehicle, so that an AC output voltage is generated in the armature coil. The AC vehicle generator is connected to a rectifier, which produces a rectified output voltage obtained by rectifying the AC output voltage generated in the armature coil in the AC vehicle generator. The rectified output voltage charges a battery equipped in the vehicle and supplies electricity to various electrical loads in the vehicle.
The rectified output terminal of the rectifier is connected to an excitation circuit that excites the field coil. The excitation circuit is connected to a semiconductor switch element that is disposed in series with the field coil. The semiconductor switch element on-off controls the field current flowing through the field coil. A voltage adjustment circuit operating based on the rectified output voltage from the rectifier turns the semiconductor switch element on and off to adjust the rectified output voltage to a level within a predetermined range independent of increase in the rotation speed of the AC vehicle generator driven by the motor. In an output voltage controller for the AC vehicle generator, a switching surge voltage is generated when the semiconductor switch element is switched between ON and OFF. The switching surge voltage varies the rectified output voltage, so that the battery and other electrical loads are undesirably affected.
In Japanese Patent No. 2,529,273, which is related art, the switching surge voltage is called switching noise. The related art proposes a voltage adjustment circuit including a slope generation circuit that generates a slope voltage that linearly changes with time, and the slope generation circuit slowly switches the semiconductor switch element between ON and OFF to reduce the switching noise.
Patent Document 1: Japanese Patent No. 2,529,273